Catalytic cracking process employing an aluminum silicon spinel-mullite-gamma alumia containing catalyst

ABSTRACT

Catalytic compositions which comprise alumina bound spinel and/or spinel-mullite mixtures having an alkali metal content of below about 0.50 weight percent, preferably below about 0.10. The compositions are obtained by calcining and caustic leaching preformed particulate composites of clay and alumina sol, preferably chlorhydrol. The catalysts are particularly useful for the catalytic cracking of heavy hydrocarbon feedstocks to obtain gasoline and light cycle oil. When used for cracking feedstocks high in vanadium content these compositions may contain added alkaline earth oxide in order to passivate the vanadium.

This is a division of application Ser. No. 063,374, filed June 18, 1987,which is a division of application Ser. No. 802,484, filed Nov. 27,1985, which is a continuation-in-part of application Ser. No. 657,859,filed Oct. 5, 1984, all now abandoned.

The present invention relates to catalysts and catalyst supports, andmore particularly to highly active catalytic cracking catalysts whichare derived from kaolin.

Catalysts used for the catalytic cracking of hydrocarbons typicallycomprise amorphous silica alumina gels, clay and/or crystallinealuminosilicate zeolites which are formed into particles of desiredshape, size and hardness. As disclosed in U.S. Pat. Nos. 3,932,268,3,647,718 and 3,657,154, silica-alumina and zeolite components used inthe preparation of catalysts may be derived from clays such as kaolin.Furthermore, as shown in U.S. Pat. Nos. 3,957,689, 3,912,619 andCanadian Pat. No. 967,136, zeolite containing catalyst compositions maycontain a substantial quantity of raw kaolin which is formed into hard,attrition resistant catalytic composites by the addition of suitablebinders such a silica, silica-alumina, or alumina sol, includingchlorhydrol.

As disclosed by Brindley and Nakahira, Journal of the American CeramicSociety, Vol. 42, No. 7, pp. 319-323, (1959) kaolinite is converted to amaterial which contains an aluminum silicon spinel when heated to about925° to 950° C. Furthermore, heating to temperatures of about 1050° C.results in the formation of a mullite phase. In both cases some of thesilica in the kaolin is converted into a caustic soluble amorphous phaseor at higher temperatures into crystobalite, a crystalline silica.

In recent years the refinery industry has been utilizing increasingamounts of heavy (residual) hydrocarbon feedstocks in the production ofgasoline and light cycle oil. These heavy feedstocks are catalyticallycracked in the presence of catalysts which must be active, resistant todeactivation by metals, attrition resistant and cheap.

Clay, and particularly kaolin, due to its availability and relativelylow cost, is a particularly attractive raw material source for theproduction of catalytic cracking catalysts which are used in substantialquantities in the processing of contaminated residual feedstocks.

It is therefore an object of the present invention to provide improvedlow cost catalysts and catalyst supports.

It is a further object to provide catalytic cracking catalysts which arederived from clays that are highly active, attrition resistant andinexpensive to manufacture on a commercial scale.

It is another object to provide low cost clay derived cracking catalystswhich may be blended with conventional zeolite containing catalysts toobtain compositions which are particularly effective for the cracking ofresidual feedstocks.

These and further objects of the present invention will become readilyapparent to one skilled in the art by the following detailed descriptionand specific examples.

Broadly, my invention contemplates catalysts and catalyst supports whichcomprise spinel-mullite-gamma alumina containing composites wherein thespinel-mullite phase is characterized as having a silica to aluminaratio of below about 1.5, and the composites have a sodium content ofbelow about 0.50 weight percent expressed as Na₂ O.

More specifically, I have found that highly active catalytic crackingcatalysts may be obtained by a process which includes the followingsteps:

(1) Clay, preferably kaolin, is mixed with basic aluminum chloride sol(chlorhydrol);

(2) The mixture is formed into particulate kaolin-chlorhydrol compositesof desired shape and size;

(3) The composites are calcined at a temperature of from about 1700° to2200° F.;

(4) The calcined composites are reacted with an alkali metal hydroxidesolution, preferably sodium hydroxide solution to remove a portion ofthe silica;

(5) The reacted composites are washed and ion-exchanged to removesoluble salts.

In a particularly preferred practice of the invention, the ion exchangedcomposites are combined with a conventional zeolite containing fluidcracking catalyst to form physical blends of the spinel-mullite-gammaalumina compositions of the present invention with conventional zeolitecontaining fluid cracking catalysts to obtain a catalyst mixture whichis particularly effective for the processing of high molecular weight(heavy residual type) hydrocarbon feedstocks.

The basic aluminum chloride sol (chlorhydrol) which is combined with theclay, possesses the general chemical formula: Al_(2+m) (OH)_(3m) Cl₆wherein m=4 to 12 is available commercially or may be prepared byreacting aluminum metal and/or alumina with hydrochloric acid asdisclosed in U.S. Pat. Nos. 2,196,016, 4,176,090 and Canadian Pat. No.967,136. The chlorhydrol solution contains from about 20 to 35 weightpercent solids and is combined with the clay, preferably kaolin, inamounts which provide a formable mixture, i.e. from about 20 to 60solids.

In a preferred practice of the invention where a fluid cracking catalyst(FCC) is prepared, a mixture comprising from about 75 to 95 weightpercent kaolin, 5 to 25 weight percent chlorhydrol as Al₂ O₃ (dry basis)and the balance water is spray dried at an inlet temperature of 500° to1000° F. to obtain microspheres having a particle size of about 20 to200 microns. The spray dried kaolin/chlorhydrol mixtures are thencalcined at a temperature of 1700° to 2200° F. for a time sufficient toconvert the kaolin clay to a spinel-mullite phase and amorphous silica,and the chlorhydrol to a cohesive gamma alumina binder. The X-raydiffraction pattern of the calcined product is similar to that ofgamma-alumina and as shown in the previously cited article of Brindleyand Nakahira, and set forth in Table A below.

                  TABLE A                                                         ______________________________________                                        Comparison of Lattice Spacings and                                            Lattice Parameters of the Spinel-Type                                         Phase from Kaolinite and of Gamma Alumina.sup.1                               Spinel-type phase                                                             In-                                                                           ten-                    Gamma Alumina                                         hkl  sity.sup.2                                                                           (1)       (2)     (1)      (2)                                    ______________________________________                                        400  S      1.971(7.884)                                                                            1.973(7.892)                                                                          1.976(7.904)                                                                           1.977(7.908)                           440  VS     1.394(7.885)                                                                            1.394(7.885)                                                                          1.397(7.900)                                                                           1.398(7.906)                           444  W      1.138(7.884)      1.141(7.905)                                    731  W                        1.030(7.911)                                    800  VW                       0.9879(7.903)                                   840  VW                       0.8845(7.910)                                   ______________________________________                                         .sup.1 G. W. Brindley and M. Nakahira, "III, The High Temperature Phase,"     J. AM. Ceram. Soc., 42(7), 319-24.                                            .sup.2 S = strong, VS = very strong, W = weak, VW = very weak.                .sup.3 Kaolinite calcined at 950° C.                              

The calcined microspheres are then reacted with an alkali metalhydroxide solution, preferably sodium hydroxide solution, that containsabout 5 to 50 weight percent NaOH, for a period of 5 to 240 minutes at atemperature of 100° to 212° F. The quantity of sodium hydroxide solutionused during the reaction ranges from 1.5 to 10 parts by weight solutionper part by weight microspheres.

During reaction with the sodium hydroxide solution, silica is removed(leached) from the microspheres to obtain a composition that containsfrom about 45 to 95 percent by weight spinel having the chemical formula0.4-2.0 Al₂ O₃.SiO₂, 0 to 50 percent by weight mullite having thechemical formula 3 Al₂ O₃ :2 SiO₂ and 5 to 25 percent by weight gammaalumina binder.

Subsequent to reaction with sodium hydroxide solution, the microspheresare washed with water to remove soluble salts, such as sodium silicate,and ion exchanged with ammonium sulfate solution to remove additionalsodium ions. In addition, the microspheres may be treated with solutionsof alkaline earth metal salt (Mg and Ca in particular) to impart a levelof alkaline earth content of up to about 10 weight percent andpreferably 1 to 5 weight percent recovered as alkaline earth metaloxide.

The finished spinel-alumina/mullite catalyst supports and catalysts havethe following characteristics:

(a) A composite alkali metal content of below about 0.50% by weight Na₂O;

(b) An alumina binder content of from about 5 to 25 percent by weightcalculated as Al₂ O₃ ;

(c) A spinel content of from about 75 to 95 percent by weight, whereinthe spinel component has the mole ratio formula 0.4 to 2.0 Al₂ O₃.SiO₂.

(d) A mullite content of from about 0 to 50 percent by weight, whereinthe mullite component has the mole ratio formula 3 Al₂ O₃.2SiO₂.

In addition, the catalyst/support compositions have the followingphysical characteristics:

(a) A surface area of from about 100 to 300 m² /g as measured by BETnitrogen absorbtion technique.

(b) A pore volume distribution which is characterized as follows:

(1) A total pore volume of from about 0.30 to 0.70 cc/g.

(2) A maximum number of pores in pores between 35 and 55 Å in diameter.

(3) Little or no pore volume in pores less than 30 Å in diameter.

(4) A pore volume distribution as follows: 0.20 to 0.50 cc/g in pores ofless than 100 Å in diameter, 0.05 to 0.20 cc/g in pores ranging from 100to 600 Å in diameter, and 0.05 to 0.30 cc/g in pores above 600 Å indiameter.

(c) Particle size:

(1) Ranging preferably from about 20 to 200 microns when the product isprepared in spray dried (fluid microsphere) form.

(2) Ranging from 0.2 to 4 mm when the composition is prepared in formsof pills, granules, extrudates and spheres for use as catalyst supports.

(3) An attrition resistance characteristic of from about 2 to 20 asmeasured by the Davison Index (DI) and 0.2 to 2.0 Jersey Index (JI) asdetermined by the methods set forth in U.S. Pat. No. 4,247,420.

(d) X-ray Diffraction Pattern:

An X-ray diffraction pattern similar to that described by Brindley(Table A) of material mostly in the silica-alumina spiral form or ifcalcined at a higher temperature may contain a high level of mullite.Typical X-ray patterns (using only the strongest peaks) for thematerials are:

                  TABLE B                                                         ______________________________________                                        SiO.sub.2 --Al.sub.2 O.sub.3 Spinel                                                                  Mullite                                                2Q      Intensity      2Q     Intensity                                       ______________________________________                                        45.8    10             26.0   10                                              67.3    10             40.8   8                                               37.3    6              60.4   8                                               39.5    6                                                                     46.5    6                                                                     ______________________________________                                    

In one preferred embodiment of the invention the cracking catalystswhich are prepared in microspheroidal form having a particle sizepredominantly in the range of from about 20 to 200 microns are used asFCC catalysts and/or blended with conventional zeolite containing fluidcatalytic cracking catalysts (FCC catalysts) in amounts ranging fromabout 2.5 to 80 percent by weight FCC catalyst. The conventional FCCcatalysts utilized in this embodiment of the invention are commerciallyavailable and typically comprise crystalline aluminosilicate zeolitessuch as rare-earth exchanged faujasite (type Y zeolites) and/or the ZSMtype zeolites and are prepared in accordance with the methods typicallydisclosed in U.S. Pat. Nos. 3,867,308 and 3,957,689. The catalystblends, particularly those containing alkaline earth metal oxide, areparticularly effective for the catalytic cracking of high molecularweight petroleum feedstocks which contain high levels of vanadium.

A more clear understanding of my invention may be obtained by referenceto the following detailed description and specific examples.

EXAMPLE 1

Clay microspheres were prepared using 10 weight percent Al₂ O₃ binderand 90 weight percent kaolin. 3,404 g basic aluminum chloride (aluminumchlorhydrol having the formula Al₂ (OH)₅ Cl) containing 23.5 weightpercent Al₂ O₃ was added to a 10 gallon tank. 8,372 g of kaolin clay wasadded with agitation and H₂ O as required to make a workable slurry.After mixing thoroughly the slurry containing about 50 weight percentsolids was spray dried at an inlet temperature of 600° F. A portion ofthis sample was calcined for 1 hour at 1800° F. and the physicalproperties at this point were: ABD/CD (average bulk density/compacteddensity)=0.95/1.04; DI/JI=1/0.2; SA (surface area)=33 m2/g. 250 g of thecalcined microspheres were added to 500 ml solution containing 125 gNaOH and boiled under reflux for 1 hour. The sample was then filtered,washed 2X1/2 liter hot deionized H₂ O, reslurried in 1/2 liter H₂ O andthe pH adjusted to 4.0 using acidified aluminum sulfate solution, aged1/4 hour at 150° F.@pH 4.0, filtered, and washed on the filter one timewith 1/2 liter hot H₂ O, one time with 1/2 liter pH 9.0 H₂ O adjustedwith NH₄), and one time with 1/2 liter hot H₂ O and oven dried. Theanalysis of this sample was Wt. % Na₂ O=0.52, Wt. % Al=75.33,ABD/CD=0.79/0.83, SA=191, DI/JI=11/0.8. 71 g (as is) of this materialwas exchanged with 35.5 g (NH₄)₂ SO₄ in 710 ml H₂ O for 1/2 hour at 150°F., filtered, washed three times with 355 ml hot H₂ O and oven dried at250° F. Microactivity tests (as determined in accordance with ASTM TestProcedure D-3907) on this sample after an 8 hour, 1350° F., 100% steamtreatment gave 36 volume percent conversion for the non-(NH₄)₂ SO₄exchanged sample and 64 volume percent conversion for the (NH₄)₂ SO₄exchanged sample. This is a very high activity for a non-zeolitepromoted catalyst.

EXAMPLE 2

This example shows the excellent hydrothermal stability of the causticleached clay microsphere. Caustic leached clay microspheres wereprepared as described in Example 1, except they were exchanged twicewith (NH₄)₂ SO₄ using 0.5 g (NH₄)₂ SO₄ /g leached product. Theproperties of this sample were: ABD/CD=0.70/0.81, DI/JI=11/1.0, Wt. %Na₂ O=0.071, Wt. % Al₂ O₃ =68.27. This sample gave 67.7% conversion in astandard microactivity test after a 2 hour @1250° F. thermal treatment,and 60.6% conversion after an 8 hour, 1350° F., 100% steam deactivation.This 90% retention of activity is exceptionally good for a non-zeolitepromoted catalyst.

EXAMPLE 3

This example shows that the unleached microsphere has very low crackingactivity compared to the leached samples prepared in Examples 1 and 2.5,320 g aluminum chlorhydrol solution (of Example 1) were added to a 10gallon tank and 10,174 g kaolin clay added with H₂ O added as requiredto make an easily pumped slurry (50 wt. % solids). After spray drying,the microspheres were calcined for 1 hour at 1800° F. After the samesteam deactivation as given to the preparations in Examples 1 and 2,this material gave 15.8% conversion in a standard microactivity test.Therefore the caustic leach substantially enhances the activity of thismaterial.

EXAMPLE 4

This example shows that blends of the caustic leached microspheres withconventional zeolite containing FCC catalyst (Components A & C) can beused to improve metals tolerance, even at identical zeolite input.Microactivity results, summarized in Table I, show significantly betteractivity retention for the 5 wt. % MgO on caustic leached clay blendthan for the base. In addition, coke selectivity (coke/unit kineticconversion) is also improved over the base.

Microspheres of the present invention (Component B) were prepared byspray drying a slurry of 15.0% by weight Al₂ O₃ from chlorhydrol and 85%by weight clay, and calcining for 1 hour at 1800° F. 1.0 Kg of thesecalcined microspheres was added to 2.0 1 of solution containing 400 gNaOH and hot aging for 11/2 hours at 175°-180° F., filtering, washing 3times with 1 l room temperature deionized water, exchanged 3 times in2.0 l solution containing 325 g (NH₄)₂ SO₄ (pH was adjusted to 7.0 onthe first exchange only with 10% H₂ SO₄). After each exchange thecatalyst was filtered, washed 1 time with 2.0 deionized water at roomtemperature (3 times after last exchange) and oven dried at 121° C.overnight. 105.5 g of this material was impregnated with 65 ml ofsolution containing 26.6 g MgCl₂.6H₂ O, dried overnight at 121° C. andthen calcined for 1 hour at 677° C.

Catalysts I and II which comprise components A(I) and a mixture ofComponents B and C(II) described in Table I was prepared and evaluatedfor resistance to metals deactivation. As shown in the data set forth inTable I, the activity retention of the catalyst II of the presentinvention containing Component B (MgO on alumina bound spinelmicrosphere) is dramatically improved relative to the unblendedconventional composition Catalyst I.

Furthermore, as shown in Table II, Catalyst IV which comprises a mixtureof Component F (an alumina bound spinel microsphere in hydrogen ionexchanged form (via (NH₄)₂ SO₄) and Component E also shows dramaticallyimproved activity retention in the presence of Ni+V or V when comparedto Conventional III which comprises Component D as described in TableII.

                  TABLE I                                                         ______________________________________                                        Effect of a Mg.sup.+2 Impregnated Caustic Leached Clay                        Blend Component on Metals Tolerance                                                         Catalyst I Catalyst II                                          ______________________________________                                                        100% A.sup.(1)                                                                             62.5% B.sup.(2)                                                               37.5% C.sup.(3)                                                  (15% Zeolite)                                                                              (15% Zeolite)                                    0.50 Wt. % Ni + V                                                             Vol. % Conversion                                                                             57.4         71.6                                             H.sub.2, wt. % Feed                                                                           0.43         0.51                                             Coke, wt. % feed                                                                              3.97         5.49                                             Coke/Kinetic Conv.                                                                            2.9          2.2                                              1.0 Wt. % Ni + V                                                              Vol. % Conversion                                                                             29.5         67.4                                             H.sub.2, wt. % Feed                                                                           0.65         0.82                                             Coke, wt. % Feed                                                                              4.95         6.88                                             Coke/Kinetic Conv.                                                                            11.8         3.3                                              ______________________________________                                         A = 13% Al.sub.2 O.sub.3 binder, 15% low Na.sub.2 O calcined rare earth Y     72% kaolin.                                                                   B = 5% MgO on a caustic leached clay microsphere.                             C = 15% Al.sub.2 O.sub.3 binder, 40% low Na.sub.2 O calcined rare earth Y     45% kaolin.                                                              

                  TABLE II                                                        ______________________________________                                        Effect of a Caustic Leached Clay Blend Component on                           Metals Tolerance                                                              Composition      Catalyst III                                                                              Catalyst IV                                      ______________________________________                                                         100% D      73.5% E                                                                       26.5% F                                          Vol. % Conversion                                                                              23.0        63.7                                             (at 0.50 wt. % Ni + V)                                                        Vol. % Conversion                                                                              25.0        62.3                                             (at 0.25 wt. % V)                                                             ______________________________________                                         D = 10.0% Al.sub.2 O.sub.3 binder, 12.5% calcined rare earth Y, 77.5%         Kaolin clay.                                                                  E = 12.5% Al.sub.2 O.sub.3 binder, 17% calcined rare earth Y, 70.5% Kaoli     clay.                                                                         F = 15.0% Al.sub.2 O.sub.3 binder, 85% caustic leached spinel prepared as     described in Example 2.                                                       Microactivity Test Conditions: 500° C., 16 WHSV, 3 catalyst/oil on     a West Texas Heavy Gas Oil after an 8 hour, 732° C., 100% steam        treatment.                                                               

I claim:
 1. A method for catalytically cracking hydrocarbons whichcomprises reacting a hydrocarbon feedstock with a catalytic compositioncomprising an aluminum silicon spinel-mullite-gamma alumina boundcomposite in which the spinel phase has a silica to alumina ratio ofabove about 0.40 and characterized by a surface area of from about 100to 300 m2/g, a total pore volume of from about 0.30 to 0.70 cc/g, thex-ray pattern set forth in Table B, and an alkali-metal oxide content ofbelow about 0.50 weight percent.
 2. The method of claim 1 wherein thehydrocarbon feedstock contains vanadium.
 3. The method of claim 1wherein said catalytic composition is mixed with a zeolite containingcatalytic cracking catalyst.
 4. The method of claim 1 wherein thecatalytic composition contains from about 0.25 to 10.0 weight percentalkaline earth metal expressed as the oxide.
 5. The method of claim 4wherein the hydrocarbon feedstock contains vanadium.